Submarine elongate structures, and in particular submarine pipelines, can become unstable through exposure to environmental influences, particularly hydrodynamic loads arising from underwater currents and wave action. These hydrodynamic loads typically increase in regions of shallow water. The combination of extreme environmental loads and shallow water are present in Australian waters, typically on the North West Shelf off the West Australian coast.
Various systems are currently utilised for submarine pipeline stabilisation, including weight coatings on pipelines, coverings on pipelines, installation of pipelines in trenches in the seabed, and securing pipelines to the seabed by way of mechanical anchors. Various deficiencies and problems can be associated with each of these stabilisation systems. For example, weight coating requirements for pipelines can be very high or impracticable. Trenching of pipelines is required to be deep in the seabed. Coverings over the pipeline need to be thick and of adequate weight, and in some cases the covering material may itself be unstable. Mechanical anchors of high capacity are required at close intervals to secure the pipelines to the seabed.
While the abovementioned systems can be utilised in many situations, there are locations where the cost involved can be very high or indeed prohibitive, and the installation procedure can be time-consuming.
A stabilisation system which seeks to address the deficiencies outlined above is disclosed in the applicant's international application WO 01/01028. While this stabilisation system has proved to be particularly effective, difficulties can be encountered in stabilising a section of a pipeline extending over certain seabed formations, particularly an area of a seabed which is sloping and also irregular. The irregularity may consist of roughness arising through, for example, the presence of rocky outcrops on the seabed.
It against this background, that the present invention has been developed.
The preceding discussion to the invention is intended only to facilitate an understanding of the present invention. It should be appreciated that the discussion is not an acknowledgement or an admission that any of the material referred to was or is part of the common general knowledge in Australia as at the priority date of the application.